Optical detection device

ABSTRACT

A diffractive optical element device for use in spectroscopy, where broadband light is emitted from a light source ( 31 ) towards the optical element ( 24 ) and from there is transmitted to at least one detector ( 29; 29 ′). The optical element has a plurality of diffractive dispersively focusing patterns, preferably partly integrated into each other, whose respective centers are two-dimensionally offset relative to each other in order to produce a plurality of spectra ( 25–28 ), where at least two are separate, but offset relative to each other and/or partly overlapping. In an alternative embodiment, the optical element consists of either one diffractive optical element ( 60 ) that is related to a wavelength and produces a spectrum, or at least two diffractive optical elements ( 60, 61 ) which are related to respective wavelengths and which produce at least two mutually partly overlapping spectra to give a composite spectrum. Means are provided on or in connection with the optical element in order to produce in said spectrum at least one indication of upper and/or lower wavelength value.

The present invention relates to a diffractive optical element devicefor use in spectroscopy, where broad-band light is emitted from a lightsource towards the optical element and from there is transmitted to atleast one detector, as is disclosed in the appended claims.

As illustrations of the prior art reference is made to. WO 9961941, U.S.Pat. No. 4,729,658, WO 0062267, WO 9634256, EP 0075171, GB 2219853, U.S.Pat. Nos. 5,369,276 and U.S. 4,391,523.

WO 9961941 relates to a diffractive optical element in two layers forincreasing the wavelength range for the purpose of correcting colouraberration (chromatic aberration). Thus, there is the same focus forblue and red, whereas the present invention in effect seeks instead todisperse the colours, and one of the ways in which this is achieved isby placing the patterns in the same plane.

U.S. Pat. No. 4,729,658 uses a grating as a diffractive optical element,but in this case the element does not provide a focusing solution.Focusing takes place with the aid of a lens. This known solutionproduces just one spectrum for each point of light, whereas the presentinvention provides several spectra for each point of light.

WO 0062267 relates to a solution which does not give any spectralresolution and no dispersive focusing either. Consequently, a pluralityof spectra are not produced.

EP 0075171 describes a standard grating spectrometer with harmonicdetection. This is a dispersive, non-focusing solution where thespectral response that hits the detector is modulated by a liquidcrystal shutter means. The solution is not focusing and nor does itproduce a plurality of spectra.

One object of the present invention is to provide a device which notonly can be used for spectroscopy in connection with a medium, as forexample gas or fluid, but also can be used for analysing a medium suchas an article of, for example, glass or plastic, and is also suitablefor use in the analysis of biological material, waste, medical samples,fluids and preparations, metals and/or alloys thereof and plasticmaterials or glass in general. Optionally, the said medium may consistof, for example, a cellular liquid.

One object of the present invention has been to construct diffractiveoptical elements for the purposes of spectroscopy. The aim has been toget a spectrum out of such a diffractive optical element, as a standardgrating would do, except that the diffractive optical element can beconstructed to have specific characteristics, as for example focusingeffect.

According to the invention, the device is characterised by the featuresthat are set forth in the appended claims.

Additional embodiments of respective alternatives of the device will beevident from the respective attached subordinate patent claims and thefollowing description.

The invention will now be described in more detail with reference to theattached drawings.

FIG. 1 shows a principle of a diffractive optical element.

FIG. 2 illustrates reflectance in connection with a diffractive opticalelement.

FIG. 3 shows source and detector location in connection with a firstembodiment.

FIG. 4 shows source and detector location relative to an optical elementaccording to a second embodiment.

FIG. 5 a shows the phase of the reflectance function before it is cutoff to obtain the profile of the diffractive optical element.

FIG. 5 b shows the distance along the profile.

FIG. 6 a shows the profile of the diffractive optical element, and FIG.6 b shows distance along the profile.

FIG. 7 shows an outer part of a Fresnel zone plate.

FIG. 8 shows a diffractive optical element profile for a two wavelengthcase.

FIG. 9 shows a general two-wavelength case associated with the profileof a diffractive optical element and related to the embodiment shown inFIG. 3.

FIG. 10 illustrates the production of a spectrum based on lighttransmitted through a Fresnel zone plate.

FIG. 11 shows a modification of the embodiment illustrated in FIG. 10.

FIG. 12 shows a variant of the embodiment depicted in FIG. 11.

FIG. 13 shows a further development of the embodiment illustrated inFIG. 12.

FIG. 14 shows yet another variant of the embodiment depicted in FIGS. 12and 13.

FIG. 15 shows the use of a diffractive optical element in connectionwith the use of reflection.

FIG. 16 shows the use of a diffractive optical element in connectionwith the use of light transmission through the element.

FIG. 17 shows the use of a diffractive optical element where either theelement or a cooperating detector is movable.

FIG. 18 shows wavelength focus dependency of a Fresnel zone plate inconnection with the part of the lens that is offset from the opticalaxis of the lens.

FIG. 19 shows intensity distribution for a Fresnel zone plate fordifferent wavelengths.

FIG. 20 shows on an enlarged scale specifications for a reflectiveplane.

FIG. 21 shows a grating outline for use as a diffractive opticalelement.

FIG. 22 shows an optical element in the form of a concave grating.

FIG. 23 shows a spectrum obtained by using a so-called blazed grating.

FIG. 24 shows a diffractive optical element having moulded reflectiveelements (see FIG. 21).

FIG. 25 shows a diffractive optical element which is offset from theideal optical axis of a Fresnel zone plate, and where one or tworeference elements are provided around the optical axis.

FIG. 26 shows diffraction patterns from the reference element fordifferent wavelengths of λ.

FIG. 27 shows a spectrum with references (see also FIG. 19).

FIG. 28 a shows invisible spectra (IV) side by side.

FIG. 28 b shows a visible and an invisible spectrum contiguous to oneanother.

FIG. 28 c shows a visible and an invisible spectrum spaced apart.

FIG. 28 d shows visible spectra spaced apart.

FIG. 28 e shows invisible spectra partly overlapping each other.

FIG. 28 f shows visible spectra partly overlapping each other.

FIG. 29 shows a visible and an invisible spectrum offset in relation toone another and in connection with detectors.

FIG. 30 shows the device according to the invention in connection with atransparent or translucent medium, for example, an article.

FIG. 31 shows a minor modification of a part of the device shown in FIG.30.

FIG. 32 shows the device in an embodiment intended for detection of amedium which has light absorption, light reflection, luminescence orre-emission properties.

FIG. 33 shows a modification of the device according to the inventionintended for detection of a transparent or translucent medium, wheredetection is based on the light absorption, light reflection,luminescence or re-emission properties of said medium.

FIG. 34 shows an embodiment of the device where the diffractive opticalelement, light source and light detector are all stationary.

FIG. 35 shows an embodiment of the device where the diffractive opticalelement is movable about one or two axes, or where the light source ismovable.

FIG. 36. illustrates possible two-way movement of a set of spectra inrelation to a light detector.

FIG. 37 shows by way of example a means for tilting a diffractiveoptical element.

FIG. 38 shows a means moving a light source.

FIG. 39 a shows an alternative means for moving a light source, and FIG.39 b shows a means for moving a detector in relation to a plurality ofspectra.

FIG. 40 shows the production of a spectrum based on light that istransmitted towards Fresnel zone plate fragments, and is a variant ofFIG. 12.

FIG. 41 shows a variant of FIG. 40.

FIGS. 42 and 43 show schematically how the Fresnel zone plate fragmentscan be manipulated mechanically or optically blanked off.

FIG. 44 shows schematically how the Fresnel zone plate fragments can beoptically blanked off.

FIG. 45 shows as a second example a means for tilting a diffractiveoptical element.

FIG. 46 shows a variant of the means in FIG. 45.

FIG. 47 shows an alternative method for disabling a diffractive opticalelement.

FIG. 48 shows a distance/intensity diagram related to this alternativemethod.

FIG. 1 shows the principle for the use of two wavelengths in connectionwith a diffractive optical element, hereinafter referred to as a DOE.The DOE images the point S1 onto D1 (wavelength λ1) and the point S2onto D2 (wavelength λ2). When there is a light source S and a detectorD, scanning the said DOE will have the effect of imaging λ₁,respectively λ₂, onto the detector at respective scanning angles θ₁ andθ₂. The problem lies in determining the profile of the said DOE havingthese characteristics. The scanning axis (i.e., the DOE's tilt angle) isindicated by SA. It may be useful to consider certain general aspects ofthe present invention. In connection with the definition of a wavefront,a source s_(n) whose location is defined by the vector r_(s) _(n)_(source) (x_(S) _(n) , y_(s) _(n) , z_(s) _(n) ), and its image d_(n)whose location is defined by the vector r_(d) _(n) _(detector) (x_(d)_(n) , y_(d) _(n) , z_(d) _(n) ) may be considered.

S_(n)(r) is the spherical wavefront coming from the source:S _(n) ^((r)) =A _(s) _(n) ·e ^(i.k) ^(n) ^(.r) ^(s) ^(n)   (1)with k_(n)=2π/λ_(n) and r_(sn)=√{square root over (x_(s) _(n) ²+Y_(s)_(n) ²+z_(s) _(n) ²)} and i=√{square root over (−1)}and where A_(s) _(n) is the wavefront amplitude at the said DOE.

D_(n)(r) is the spherical wavefront which is focused on the detector anddefined by the equation:D _(n)(r)=A _(d) _(n) ·e ^(−i.k) ^(n) ^(r) ^(d) ^(n)   (2)with r_(dn)=√{square root over (x_(d) _(n) ²+Y_(d) _(n) ²+z_(d) _(n)²)}, and where A_(d) _(n) is the wavefront amplitude at the said DOE.

It should be noted that the wavefront intensity of S_(n)(r) isI _(s) _(n) =|S _(n)(r)|² =S _(n)(r)·S _(n)(r)*=A _(d) _(n) ². Andsimilarly, I _(d) _(n) =A _(d) _(n) ².  (3)

The DOE optical reflectance function is given by the equationt(r)=A ₀ ·e ^(−i.k) ^(n) ^(.2ƒ(r))  (4)where f(r) denotes the DOE profile function, k_(n)=2π/λ_(n), and λ_(n)is the wavelength of the incoming wave S_(n).

Here, it is assumed that the phase delay caused by reflection on thesaid DOE is a pure geometric addition to the optical path length.

Given Fourier optics, it is possible to write:Outcoming waves=S _(n)(r)·t(r)  (5).

It may also be useful to consider more closely the theory related to adiffractive optical element. The single wavelength case can be taken asa starting point.

The source S₁ emits light at wavelength λ₁ and is imaged on d₁. Givenequations 4 and 5, the following is obtained:

$\begin{matrix}{{{Outcoming}\mspace{20mu}{wave}} = {D_{1} = \left. {S_{1} \cdot {t(r)}}\Leftrightarrow{t(r)} \right.}} \\{= \left. {D_{1} \cdot \frac{S_{1}^{*}}{{S_{1}}^{2}}}\Leftrightarrow{t(r)} \right.} \\{= {\frac{A_{d1}}{{\underset{\_}{A}}_{s_{1}}} \cdot {\mathbb{e}}^{- {{\mathbb{i}}.{k_{1}{({r_{s_{1}} + r_{d_{1}}})}}}}}} \\{A_{0} \cdot {\mathbb{e}}^{{- {{\mathbb{i}}.k_{1}}}{.2}{f{(r)}}}}\end{matrix}$

Solving this equation results in

${f(r)} = {\frac{{mod}\left\lbrack {{k_{1} \cdot \left( {r_{s_{1}} + r_{d_{1}}} \right)},{2\pi}} \right\rbrack}{2 \cdot k_{1}}.}$

This characterises the remainder of an integer function (modulofunction) where in general mod [a,b,] gives

${f(r)} = {\frac{a}{b} - {\frac{a}{b}}}$

The following system geometry which is shown in FIG. 3 where SA asbefore indicates the scanning axis may now be considered. FIG. 3 is alsorelated to that which can be seen from and will be described inconnection with FIGS. 5, 6 and 7. FIGS. 5 a and 5 b show the phase forthe reflectance function t(r) before it is cut off to obtain the DOEprofile, and where FIG. 5 a indicates the function r_(s) ₁ +r_(d) ₁ ,and where FIG. 5 b indicates distance along the DOE profile.

FIG. 6 a shows the DOE profile which in this case is a central part ofthe Fresnel zone plate. FIG. 6 b shows the distance along the profile.The result is per se in accordance with expectations. Nevertheless, thecentral part of a Fresnel zone plate is known to givewavelength-independent direction dispersion, so that any wavelengthcoming from the source would focus at the same location on the detector.By shifting the source S and the detector D to the left, see FIG. 4, theDOE profile will then be the off-axis part of a Fresnel lens as shown inFIG. 7, which thus shows the outer part of the Fresnel zone plate. Thisprofile is now wavelength-dependent, and a wavefront having wavelengthλ₁ coming from the source is imaged on the detector, and the otherwavelengths will focus on different locations. This also applies ingeneral to multiple wavelength cases and the chosen geometry is as shownin FIG. 3.

A brief description will now be given of the two wavelength case whereit is simultaneously desirable to image s₁ (wavelength λ₁) on d₁ and s₂(wavelength s₂) on d₂. The DOE optical reflectance should then be:

$\begin{matrix}{{t(r)} = {{D_{1}\frac{S_{1}^{*}}{{S_{1}}^{2}}} + {D_{2}\frac{S_{2}^{*}}{{S_{2}}^{2}}}}} & (6)\end{matrix}$

Here, consideration may be given to one particular case as shown in FIG.8 where r_(s) ₁ =r_(s) ₁ and r_(d) ₂ =r_(d) ₂ . Two wavelengths λ₁ andλ₂ coming from the source S are imaged on the detector D. FIG. 8 thusshows the DOE profile in this case. It can be seen that it resembles atype of mixed patterns between two Fresnel zone plates.

The other example can be seen from FIG. 9 where the calculation has beenbased on that which is evident from the geometry in FIG. 3. The resultgiven here will be easier to interpret as two mixed Fresnel zone platesand the curves separating the two Fresnel zone plates have differentradii. However, all these curves are tangent to the direction of thescanning axis (the axis in the X direction).

Further aspects of the present invention will now be described in moredetail, starting from FIG. 10 where light is emitted from a source sthrough a diffractive optical element DOE, in this figure indicated bymeans of the reference numeral 1, towards a detector D which is capableof detecting the spectrum 2 that is produced.

By, for example, turning the element 1 about the axis y, the spectrum 2will move relative to the detector D.

FIG. 11 shows a modified diffractive optical element 3. When light issent towards the element 3, preferably from a point source and is eithertransmitted through the element 3 or is reflected thereby, a spectrum 4in a plane parallel to the element 3 will be produced, and it will beseen that this is not wholly rectangular, which is due to the prevailinggeometry. Alternatively, a spectrum 5 which is parallel to the z-axiscan be produced. Here, it will also be appreciated that if a detector 6or a detector 7 is provided, the spectrum 4 or 5 will shift when theelement 3 is subjected to a tilting motion. In this way, the detector 6or 7 can detect the actual location of said spectrum.

If this principle is taken further, as shown in FIG. 12, and where aplurality of diffractive optical elements 8, 9, 10 and 11 are provided,it will be seen that each of these produces respective spectra 12–15.The detection region of the detector 16 is indicated by the referencenumeral 17. It will be understood that although just one detector 16 isshown, there could be two or more detectors in the detection region 17.

The elements 8–11 show solely as an illustration typical axis-offsetFresnel zone plate fragments, and although on the drawing these appearto be identical, it will be understood that they must be different fromone another in order to obtain the alleged desired effect according tothe invention.

If the elements 8–11 are tilted collectively about the x-axis, the saidspectra 12–15 will move transverse to the detector field 17. However, ifthe elements 8–11 are tilted about the y-axis, the said spectra 12–15will move together along the detector field 17 and successively pass thedetector 16. Thus, it will be appreciated that for an effectivedetection of the spectra 12–15, either the detector 16 must be movedalong the field 17 or the elements 8–11 must be tilted about the y-axisso as to pass over the detector 16 successively with a respective regionof the said spectra. If, for example, more than one detector is used, adetector like detector 16′ can be provided.

With further reference to FIG. 13, it will be seen there that thediffractive optical element 18 is divided into a plurality of smallerdiffractive optical elements 19, of which only a small number are shownfor the sake of clarity. It will be seen that some of the diffractiveoptical elements 19 form certain parts of a spectrum, whilst others willform other parts of a spectrum when light illuminates the element 18.Thus, FIG. 13 can be considered to be composed of a plurality ofelements, like those of the type of elements 8–11 shown in FIG. 12. Inthis way, a whole diffractive optical element 18 is obtained which has aplurality of diffractive dispersive element patterns 19, preferablypartly integrated into one other, whose respective centres are, as isevident from FIG. 13, two-dimensionally offset relative to each other inorder to produce a plurality of spectra, where at least two areseparate, but offset relative to each other and/or partly overlapping.From FIG. 13 it will be seen that the spectra 20–23 shown in the figureare separate and offset relative to each other, but not necessarilyoverlapping.

FIG. 14. shows a further step towards integrating the differentdiffractive optical elements into a composite element, like thediffractive optical element indicated by the reference numeral 24 inFIG. 14. It will be seen that in the illustrated example this element,when exposed to light, generates four spectra 25–28. The optical element24 thus has a plurality of diffractive, dispersively focusing patterns,preferably partly integrated into one another, whose respective centres,as can also be seen clearly from FIG. 12 and also from FIG. 14, aretwo-dimensionally offset relative to each another, so that saidplurality of spectra 25–28 are produced, where at least two of these areseparate, but offset relative to each other. One or more detectors 29,29′, 29″ can be provided with an associated detection field 30. When theoptical element 24 is caused to rotate about at least a first axis y,the said at least one detector 29, 29′, when the element 24 is tilted,will be caused to detect a first set of different spectral rangesindicated by respective reference numerals 25′, 26′, 27′, 28′ inrespective ones of said separate spectra 25–28. It is also conceivablethat the element 24 could be rotatable about a second axis x which isorthogonal to the first axis y, so that said at least one detector 29,29′ upon said tilting is caused to detect at least a second set ofdifferent spectral ranges in respective ones of said spectra 25–28, thedetection field 30 remaining unchanged in the z direction, whilst thetilting of the optical element 24 about the axis x causes the saidspectra 25–28 to be shifted slightly transverse to the detection field22, i.e., in the direction of the z-axis. An alternative to moving theelement 24 about a first axis y is, of course, to keep the opticalelement 24 still and instead move the detector or detectors 29, 29′ inthe x direction, i.e., transverse to the spectral bands 25–28 of thesaid separate spectra. In addition, it will also be possible to move thedetection field with the detectors 29, 29′ and optionally more or fewerdetectors in the direction along the said spectral bands 25–28.

A further alternative would be to make the position of a light source 31adjustable in the direction of said spectral bands, in order thereby tochange the position of the detectors or the position of the detectionfield relative to said spectra 25–28. However, it is noted that both thedetectors 29, 29′ and the light source 31 are connected to electricalconnections which may make it inconvenient to mechanically shift theirpositions, whilst the element 24, on the other hand, does not have anyactive parts and thus is easier to move.

The light source 31 will preferably emit light through a fixed,preferably small aperture 32 (see FIG. 38) and a rotating disc 33 can beprovided with at least one slit 34 or a plurality of minute holes, sothat light can pass through the slit or the said holes whilst theslit-or holes, because of their arc-shaped arrangement on the disc,travel across the length of the aperture 32 as the disc rotates.

As an alternative, the light source, indicated by means of the referencenumeral 35 in FIG. 39 a, can emit light via an optical fibre 36 which ismechanically movable, for example, by exciting a piezoelectric element37 to which the end portion 36′ of the optical fibre is attached. Asindicated in FIG. 29, there can optionally be provided at least twodetectors, such as detectors 38 or 39 shown in FIG. 29 in the directionof the spectral bands of the spectra. The output from the said at leasttwo detectors may optionally be collected by time-multiplexing.

It is also conceivable that this principle involving the use of anoptical fibre or light guide can be used on the detector side, asindicated in FIG. 39 b where a detector 122 via a light guide 123 scansat least two spectra 125 lying in the focus plane of the end 123′ of thelight guide, and where a means 124, for example, a piezoelectricelement, when excited, causes the end portion 123′ of the light guide tomove either across the said spectra or optionally along said spectra.

As previously indicated, it would be advantageous to allow thediffractive optical element to be subjected to a tilting motion so as toeffect scanning through the desired parts of the separate spectra. FIG.17 outlines this in more detail, where the reference numeral 40designates a diffractive optical element, and where the light source,which optionally emits its light via a slit as previously described, isindicated by means of the reference numeral 41. The detector isindicated by the reference numeral 42. The diffractive optical element40 has its centre of tilt preferably at an end portion thereof, asindicated by the centre of tilt 43. In this solution, the desired,measured wavelengths will be focused on a curve 44, so that they hit thedetector in the centre when scanning takes place through an angle θ. Itshould be noted, however, that the spectrum in the plane is notnecessarily continuous as can be seen in a grating spectrometer, butwill consist of predefined wavelengths, and these wavelengths do notneed to be in rising or falling order. This is also in a way shownclearly in, for example, FIG. 14. The intensity of the measured spectrumas a function of the scanning angle θ can be seen clearly at the top tothe right in FIG. 17.

As previously indicated, it is conceivable that the diffractive opticalelement is based on either reflection of light or transmission of light.Gratings will either modulate the amplitude or the phase of an incidentray of light. A phase grating will give the highest diffractionefficiency. Moreover, this type of diffractive element could easily bereplicated in a compact disc substrate in large quantities by pressingor another form of replication, i.e., at low individual cost.

The case in FIG. 15 will first be described. Given that Pr(x) representsthe grating element profile, n is its refraction index and the constant

${k = \frac{2\pi}{\lambda}},$the phase profile produced by a grating of this kind will beΦ_(grating)(x)=−2k·Pr(x).

The tilting of tile incident field (respectively the grating) will havethe following effects:Φ_(tiltfield)(x)=−k·x·sin(α)Φ_(tiltgrating)(x)=2k·x·sin(β)Finally:Φ_(Re flective)(x)=Φ_(Grating)+Φ_(tiltField)+Φ_(tiltGrating)

Similarly, for that shown in FIG. 16 the following is obtained:Φ_(grating)(x)=k·(n−1)·Pr(x)

The tilting of the incident field (respectively the grating) will havethe following effects:Φ_(tiltField)(x)=k·x·sin(α)Φ_(tiltField)(x)=−k·x·sin(β)Finally, the following is obtained:Φ_(Transmission)(x)=Φ_(Grating)+Φ_(tiltField)+Φ_(tiltGrating)

It will be noted that the signs for the reflection case are the oppositeof the transmission case, since the propagation is towards the negativez values.

If a structure is set up in fraction form where n≈1.5, the following isobtained:

$\frac{\Phi_{{Refl}.{grating}}}{\Phi_{{Transm}.{grating}}} = {\frac{2 \cdot k \cdot {\Pr(x)}}{\left( {n - 1} \right) \cdot k \cdot {\Pr(x)}} = {\frac{2}{n - 1} \approx 4}}$

From this it may be concluded that the same grating profile Pr(x)generates a phase function Φ(x) which is four times greater in thereflective grating than for the transmission grating case. A tilt angleθ of the transmission grating will shift the spectrum by an angle ofless than θ, whereas an angle tilt at an angle θ for the grating case ofa reflective grating will shift the spectrum through an angle of 2θ. Thescanning in wavelength thus requires a tilt of a transmission gratingthat is more than twice that required for a reflective grating. Thus, inthe case of the present invention, it will be advantageous to apply theprinciple of the reflective grating, although a grating solution for adiffractive optical element based on transmission is of course alsopossible.

In FIGS. 15 and 16, the incident light field is indicated by the lettersIF and the optical element or the grating is indicated by the referenceDOE.

Tilting of the diffractive optical element can be effected, for example,by using a construction as shown in FIG. 37. A coil 45 is excited by apulsing or periodically varying voltage U and will manipulate an anchor46 fastened to a tiltable plate 47 to which the diffractive opticalelement, here indicated by the reference numeral 48, is attached. Inthis way, the diffractive optical element 48 will tilt about centres oftilt 49, 49′.

Alternative solutions to that shown in FIG. 37 are of courseconceivable, for example, by using a piezoelectric element which cancause a tilting motion, or by attaching the diffractive optical element48 to a condenser plate that is subjected to vibrations.

As previously indicated, it would be useful to use a part of a Fresnelzone plate which is offset from the optical axis of the Fresnel zoneplate in order to obtain diffraction.

FIG. 18 shows wavelength focus dependency for a Fresnel zone plate. Therays are drawn only for the part of the Fresnel zone plate that isoffset from its optical axis. Here, a focal plane having wavelength 1.7μm (plane 1 in FIG. 18) can be taken as a starting point. In this plane,the wavelength of 1.7 μm focuses on the optical axis, whilst thewavelengths of 1.6 μm and 1.8 μm are slightly defocused and off-axis.Here, it can be concluded that the off-axis part of the Fresnel zoneplate acts as a dispersive element with a focusing effect.

FIG. 19 shows the intensity distribution in the plane 1 for differentwavelengths when using a 3 mm off-axis part of the Fresnel zone plate.The integrated energy at a detector in the wavelength range 1.64 μm–1.76μm is constant in FIG. 19. If, for example, a 3 mm×10 mm elementoptimised for 1.7 μm is used, the intensity will inevitably be reducedat other wavelengths. The squares indicated in broken lines in FIG. 19symbolise detectors which may be about 300×300 μm² in size. The detectorsize indicated here limits the resolution to 25 nanometers. A smallerdetector would inevitably give a higher resolution of the indicatedwavelength of 1.7 μm. The values given should thus simply be understoodas examples which illustrate these aspects of the invention.

A diffractive element of this kind is shown in more detail in FIGS. 20and 21 where typical, yet for the invention non-limiting, dimensions aregiven. There are two reflective planes 50, 51 in connection with thediffractive optical element 52. The two reflective planes 50, 51 forrespective reference markings 1.6 μm and 1.8 μm in the chosen examplefunction in effect like a mirror. Their slopes are calculated so thatthe light reflected on these planes will focus on the location for the1.6 μm and 1.8 μm rays. It is also conceivable that the diffractiveoptical element or the grating could be provided with engraving on aconcave substrate 53 in order to form a grating 56 or optical element,and where the substrate conjugates a slit 57 to the detector (notshown), see FIG. 22. The distance between the slit and the grating inthe chosen example is shown to be d=50 mm and the radius of the concavesubstrate should thus be 50 mm. In this configuration, an intermediatelens is dispensed with, and the reflective planes 50, 51 as shown inFIGS. 20 and 21 thus become tilted concave mirrors. FIG. 24 shows thedesign described in connection with FIGS. 20 and 21 where it will beseen that the spectrum imaged by means of the reflective planes for thereferences 1.6 μm and 1.8 μm are given references at certain parts ofsaid spectrum, so that a detector can quite unequivocally determinewhere in said spectrum there is, for example, a signal peak. Here, itwill be seen that a lens 58 has been used, which was avoided in thesolution shown in FIG. 22. For a reflecting diffractive optical elementwithin the range of 1.6 μm to 1.8 μm and for a given grating or element,the spectrum which is generally obtained will be produced as indicatedin FIG. 22. Although it is possible to use reflective planes 50, 51 inconnection with a diffractive optical element, it is also possible touse spherical mirrors or a Fresnel zone plate centre region to providethe said references for 1.6 μm and 1.8 μm in the chosen example. Thediffractive optical element for producing a desired spectrum will beoff-axis relative to the optical axis of an ideal Fresnel zone plate.This is more evident from FIG. 25. The reference elements in FIG. 25 areindicated by the reference numeral 59 and the diffractive opticalelement which is off-axis is indicated by the reference numeral 60. If aspherical mirror is used for the reference elements 59, it will have theadvantage that such mirrors are achromatic. FIG. 26 shows in thisconnection the diffraction pattern for a central Fresnel zone platewhich acts as a reference for λ in the range 1.2–2.0 μm and with aresolution of about 30 nanometers.

The total reference intensity will be the sum of all these contributionsand its peak intensity will correspond to the intensity of the centralray at λ=1.7 μm (see FIG. 19). The plot in FIG. 19 now becomes the sameas that seen in FIG. 27, i.e., with clear markings for the wavelengths1.6 μm and 1.8 μm respectively. By making a mosaic of differentelements, it is possible to make the intensity distribution moreuniform. However, the drawback of such a solution is a more asymmetricaldistribution of each wavelength, which means, for example, that λ=1.8 μmwill have small contributions from 1.77 μm and 1.83 μm. It will bepossible to reduce the intensity by unfolding the dispersive effect inthe x-axis direction for a diffractive optical element which, forexample, is 1 mm×10 mm, and also the geometrical effect of using a 10 mmpart of a Fresnel zone plate in the y-axis direction, so that thereduction in intensity can be calculated. If such an element isoptimised for, e.g., 1.7 μm, the intensity at 1.6 and 1.8 μm will bereduced to 50%. This can be verified by calculating the amount of energycone that geometrically hits the detector in the y direction, asdifferent wavelengths have different focal lengths in the y direction.To reduce the variation, three different elements, each 1 mm and withdifferent design wavelengths, are put together in a mosaic. Thereduction at 1.6 and 1.8 μm will then be only 15%, giving a rather flatresponse over the wavelength region that is of particular interest. Likethe solution described above, the optical element can be tiltable in atleast a first plane, so that said at least one detector which will beinvolved when the element is tilted will be caused to detectsuccessively different spectral regions in said spectra or a compositespectrum. A composite spectrum can be obtained by using severaldiffractive optical elements 60, 61. This may be an advantage in orderto obtain a spectrum of maximum uniformity over the wavelength range inquestion. As an alternative, the said at least one detector, as forinstance the detector 62 shown in FIG. 24, can be movable along thespectral bands of said spectra or composite spectrum. However, assuggested earlier, it will be more preferable to use a tiltable opticalelement instead of moving the detector.

In FIGS. 28 and 29, IV denotes invisible spectrum, whilst V indicatesvisible spectrum. For the two primary alternative embodiments of theinvention, the said spectra can lie in a visible and/or an invisiblespectral range. The said spectra may thus be selected from the groupconsisting of: invisible spaced apart spectra; visible spaced apartspectra, invisible contiguous or partly overlapping spectra; visiblecontiguous or partly is overlapping spectra; visible and invisiblespaced apart spectra and invisible and visible contiguous or partlyoverlapping spectra.

In connection with, for example, colour detection, it may beadvantageous to use at least two overlapping visible spectra, asindicated in FIG. 28 f, in order to be able to detect composite coloursin the visible spectrum V. This can be provided, for example, by usingtwo inter adjustable diffractive optical elements.

In connection with, for instance, the visible spectrum, for example, forcolour detection, it may be advantageous to use several detectors 38,whereas in the invisible spectrum a smaller number of detectors 39 canbe used, as indicated in FIG. 29.

Practical solutions in connection with the present invention will now bedescribed in more detail with reference to FIGS. 30–34.

FIG. 30 shows a light source 63 which can emit light towards areflective element 64 for focusing light towards a slit 65 in anapparatus housing 66 where the light in the chosen, non-limiting examplehits a lens 67 and moves towards the dispersive optical element 68, fromwhere light is guided towards a detector 69. The lens 67 and the element68 may optionally be replaced by a dispersive, focusing, diffractiveelement (DOE). The slit 65 will preferably be small in size, as forexample, yet non-limiting, in the order of 0.3×3 mm. It is also possibleto allow the slit to be replaced by a rectangular, polygonal, round oroval aperture. Specific use of this solution may be relevant inconnection with the embodiment shown in FIGS. 12–15. The detector 69can, for example, be 0.3 mm in size. The actual housing 66 may, forexample, be 60 mm×10 mm, although this should by no means be understoodas defining the limits of the invention. To be able to limit lightscatter, baffles 70 are placed in the housing 66, as shown in FIG. 31.

To be able to tilt the diffractive optical element about a tilt axis 71,a piezoelectric element 72 is provided at a second end of the element68, as shown in FIG. 31, so that when the element 72 is excited, theelement 68 will tilt about the point 71. A transparent or translucentmedium, for example, fluid or article 73, can be introduced in the lightpath between the light source 63, 64 and the detector 69. Here, thespectrum or spectra that are displayed and detected by the detector 69will be a function of the light absorption properties of said medium 73.

A variant is outlined in FIG. 33 where the optical element is indicatedby the reference numeral 74, the light source by reference numeral 75,the apparatus housing by reference numeral 76 and the detector byreference numeral 77. As an alternative to the light source 75, anexternal light source 75′ may be provided as shown in broken lines, andwhich via an aperture 75″ in the housing 76 achieves the same as thelight source 75. Light is emitted from the light source 75 via thediffractive optical element 74 via a slit 78 in the apparatus housing 76towards a reflective element 79, so that the rays of light forming aspectrum hit the detector 77. In this case, it will be possible tointroduce a transparent or translucent medium 80 in the light pathbetween the optical element 74 and the detector 77, so that the spectrumor spectra displayed and detected by the detector 77 will be a functionof the light absorption properties of said medium 80. In the event thatthe said medium, instead of being transparent or translucent, isessentially light-reflective, as indicated in FIG. 32, alight-reflecting medium 83, for example, fluid or an article, can beintroduced into the light path between a light source 81 which has itslight reflected by a reflector 82, and the optical element 68. Saidmedium 83 will thus reflect the light towards the optical element 68 viaa lens 84 and the slit 65. The spectrum or spectra which thus aredisplayed and detected by the detector 69 will be a function of thelight absorption and/or light reflection properties of said medium 83,and/or the luminescence or re-emission properties of said medium.

In connection with the embodiment shown in FIGS. 30 and 33, it will beunderstood that not only light absorption properties will be detectable,but also light reflection properties.

In the solutions shown in FIGS. 30–33, it is conceivable that thespectrum or spectra displayed may be a function of the luminescence orre-emission properties of the said medium. In this connection, it isenvisaged specifically that the said medium may be a cellular liquid.

However, it is also possible that the said medium may consist of atleast one of the following elements:

gas, biological material, composite waste, fluids, medical samples andpreparations, foods, paper products, wood products, metals and/or alloysthereof, plastic materials, glass or articles of plastic or glass, e.g.,beverage packaging.

In the case shown in FIG. 33, it is also possible to envisage that thesaid medium may, for example, be a gas, so that the housing 76, forexample, is filled with this gas. In this case, it will be theabsorption properties of the gas in particular that will be of interest.

It is also possible that instead of moving the diffractive opticalelement, such as the element 85, shown in FIG. 34, in the light pathbetween light source 86 and detector 87, a tiltable mirror 88 isprovided. At a first end portion, the mirror 88 is pivotally mounted ata pivot point 89 and at second end it is connected to, for example, apiezoelectric element 90 which, when excited, will cause the mirror 88to tilt about the point 89. Of course, it is possible that with somesmall modifications the light source 86 and the detector 87 can switchplaces without greatly affecting the measurement data obtained. It isthus conceivable that a tiltable mirror can be placed in the light pathbetween the light source 86 and the diffractive optical element 85and/or between the diffractive optical element 85 and the detector 87.

FIGS. 35 and 36 illustrate the principle for the tilting and optionallythe rotation of an optical element 91. A tilting of the element 91 inthe direction of the arrow 92 will result in the spectra 95–98 moving indirection 92′, and rotation of the element in the direction of the arrow93 will result in the spectra 95–98 moving in direction 93′. Thus, itwill be understood that it is possible by tilting in direction 92 tocause a predetermined region of a respective spectrum 95–98 to besuccessively passed over a detector 94, whereas rotation in thedirection of arrow 93 will cause a respective other region of eachspectrum 95–98 to be passed over a detector when the tilting indirection 92 takes place about a tilt axis 99.

FIG. 40 shows a light source 100 which transmits light towards aplurality of diffractive optical elements 101, 102, 103 and 104 in theform of Fresnel zone plate fragments. A spectrum is produced from eachelement, but for the sake of simplicity and clarity only two spectra 105and 106 from the elements 104 and 101, respectively, are shown. It willbe seen that the spectrum 106 lies to the side of the spectrum 105 andis also indicated more faintly, which indicates that the spectrum is outof focus in relation to the dark field 109 which represents a lightdetector. It is also seen that the elements 101, 102 and 103 areindicated more faintly than the element 104, which is due to these tothree elements having been mechanically manipulated or optically blankedoff in such a way that the light from the light source 100 will generateeither a spectrum that is out of focus or a virtually non-visiblespectrum. This means that in reality each spectrum is investigatedsuccessively not by tilting all the elements about, for example, they-axis, but instead by bringing the elements 101–104 into such aposition that each of them successively produces a spectrum which is infocus, whilst the others are out of focus, whereby such a spectrum thatis in focus becomes clearly visible to the detector 109, whilst otherspectra remain as they are so that they do not have major impact on thedetection carried out by the detector 109.

FIG. 41 shows a light source 100 which transmits light towards aplurality of diffractive optical elements 101, 102, 103 and 104 in theform of Fresnel zone plates fragments. A spectrum is produced from eachelement, but for the sake of simplicity and clarity only two spectra 107and 108 are shown from the elements 101 and 104 respectively. It will beseen that the spectrum 108 lies behind the spectrum 107 and is alsoindicated more faintly, which indicates that the spectrum is out offocus in relation to the dark field 109 which represents a lightdetector. It will also be seen that the elements 102, 103 and 104 areindicated more faintly than the element 101, which is due to these threeelements having been mechanically manipulated or optically blanked offin such a way that the light from the light source 100 will generateeither a spectrum that is out of focus or a virtually non-visiblespectrum. This means that in reality each spectrum is investigatedsuccessively not by tilting all the elements about, for example, they-axis, but instead by bringing the elements 101–104 into such aposition that each of these successively produces a spectrum which is infocus, whilst the others are out of focus, whereby such a spectrum thatis in focus becomes clearly visible to the detector 109, whilst otherspectra remain as they are so that they do not have a major impact onthe detection carried out by the detector 109.

FIG. 42 shows diffractive optical elements 110, 111 (respectively DOE1and DOE2) each lying sealed against a respective pressure chamber 112,113 where, for instance, respective negative pressure −ΔP1 and −ΔP2 canbe supplied at time intervals, so that a spectrum generated by, forexample, the element 110 is brought out of focus when a negativepressure is applied to the chamber 112, whilst the pressure chamber 113has nominal pressure, so that a spectrum produced by the element 111will then lie in focus for the detector 109 for the part of the spectrumthat is to be investigated.

A similar reasoning applies to the embodiment in FIG. 43 where thediffractive optical elements (DOE1 and DOE2 respectively) are indicatedby the reference numerals 114 and 115. In this case, instead of pressurechambers, electrically actuatable means 116 and 117 are used, which onthe supply of drive voltage V1 and V2 at different times cause, forexample, the downward bending of the respective element. The means 116and 117 can, for example, consist of piezoelectric elements orelectrostatic elements, is whereby the bending up or down of the opticalelements will take place depending upon drive voltage supplied. When theelectrostatic principle is applied, one part of such a means will befastened to the optical element, whilst a second part will be fastenedto a base 126.

When a piezoelectric element is used, it will lie between the opticalelement 114, 115 and the base 126. If the optical element, for example,is supported at only one edge and at another can be held by said means,the optical element can in fact be tilted relative to the x or y-axis,which means that it is possible to shift the spectrum produced eithersideways or in the longitudinal direction of the spectrum. This may beeffective either for testing different colour combinations in spectrumthat partly overlap in the longitudinal direction or to bring a spectrumoutside a detection field.

FIG. 44 shows diffractive optical elements (DOE1 and DOE2 respectively)designated by the reference numerals 118 and 119. In this case, theelements are covered by light valves LV1 and LV2, designated by thereference numerals 120 and 121. The light valves are activated(addressed) at different times, so that only one of the elements at atime is capable of generating a spectrum when illuminated from a lightsource.

In those cases where it may be favourable to consider both an IRspectrum and colours simultaneously, it will be expedient to use severaldetectors. An example of this is given in FIGS. 12 and 14 where at leastone further detector 16″, respectively 29″ is added, which lies outsidethe detection field 17, respectively 30. It is also possible to envisagethe detectors lying in different y positions owing to different focusingdifferences of an IR related spectrum and a typical colour spectrum.

The solution shown in FIG. 41 where the different, generatable spectrawould have been almost superimposed if all the elements 101–104 hadgiven similarly focused spectra simultaneously, permits in reality thatmany possible colour combinations of, for example, a medium such as anarticle, can be examined by combining two or more spectra, i.e., atleast two elements produce their respective spectra which aresuperimposed on one another, but which are offset relative to eachother.

FIG. 45 shows by way of example a means 127 for moving a DOE 129, wherethe device 127 has a beam structure 127′ or similar, for example, asilicon beam, which is adapted to bend in response to power supply viaterminals 128′ to a power circuit 128 which causes the beam to bend as aconsequence of heat generation. The power circuit 128 may optionally bereplaced by piezoelectric or electromagnetic elements.

FIG. 46 shows by way of example a means 130 for moving a DOE 132 byusing a capacitive element 131, 131′ which receives voltage supply viaterminals 131″, 131′″, so that there is capacitive attraction orrepulsion, and thus movement of the beam 130′, for example, a siliconbeam.

Several alternative solutions are shown in the description and thedrawings for activating or deactivating certain diffractive opticalelements (fragments or parts) by mechanical manipulation of the element.FIG. 47 shows an alternative solution where the aim, in particularwithin the concept according to the present invention, is to be able toswitch on and off various parts of a binary hologram by changing thespacing between upper, first and lower, second reflective surfaces. Theprinciple is known per se from optical modulators, cf., for example,U.S. Pat. No. 5,311,360, where the spacing between an upper plane ofreflective beams and a lower reflective plane is changed to deactivateand activate the diffraction effect of a diffractive optical element.

It is conceivable that an upper, reflective part 133 of a binarydiffractive optical element can be made in the form of a metallisedpattern 134 on a glass plate 135, and where the lower part of the binaryformed diffractive optical element is only a reflective surface. Theterm “binary” is understood to mean an element where the relief heightmay only have two levels. The lower reflective surface may, for example,be a thin, metallised membrane 136, and the membrane may be mounted withλ/4 spacers. By, for example, applying an electric field, it will bepossible to pull the membrane towards the metallised pattern 134,thereby changing the spacing from nλ/2+λ/4=>ON to nλ/2=>OFF, where n=0,1, 2, 3 . . . .

In this way the diffractive optical element (optionally with itsfragments or parts) will be deformable so that, for example, at 0λ/16the element has in reality only a reflecting surface. The diffractionefficiency will thus be affected by, for example, the introduction of anelectric field between the membrane 136 and the plate 135, and, forexample, a stepwise adjustment of the field can be provided and thus acorresponding change of the diffraction efficiency. The diffractionefficiency of the element will be greatest at nλ/2+λ/4, and smallest atnλ/2, n=0, 1, 2, 3 . . . . The diffraction efficiency of the element ina period equal to λ/2, from mλ/2 to (m+1)λ2, where m=0, 1, 2, 3, 4 . . .follows an approximate Gaussian curve, where the maximum is half way.Advantageously, the nominal spacing can be variable in steps between 0λand 4λ/16, each step being, e.g., λ16.

It is clear from FIG. 48 that the diffraction efficiency will be cyclicwith periodicity of about 0.5λ.

1. A diffractive optical element device for use in spectroscopy, whichcomprises a light source for emitting broad-band light, a diffractiveoptical element towards which the light is emitted, and at least onedetector for receiving the light transmitted by the diffractive opticalelement, characterised in that the diffractive optical element has aplurality of diffractive, dispersively focusing patterns which form onepattern plane or several non-overlapping pattern planes, wherein therespective centre of each of said pattern planes, having an optical axisat the centre, at a location where the optical axis extends through aplane of the pattern and wherein its related optical axis beingtwo-dimensionally offset relative to each other in order to produce aplurality of spectra where at least two spectra are selected from thegroup consisting of: separate spectra offset relative to each other,separate spectra partly overlapping, and separate spectra offsetrelative to each other and partly overlapping.
 2. A diffractive opticalelement device as disclosed in claim 1, characterised in that saidplurality of patterns are partly integrated into each other.
 3. Adiffractive optical element device as disclosed in claim 1,characterised in that the diffractive optical element is tiltable aboutat least a first axis, so that when the diffractive optical element istilted, said at least one detector is caused to detect a first set ofdifferent spectral regions in respective ones of said separate spectra.4. A diffractive optical element device as disclosed in claim 3,characterised in that the diffractive optical element is tiltable abouta second axis that is orthogonal to the first axis, so that when thediffractive optical element is tilted, said at least one detector iscaused to detect at least a second set of different spectral regions inrespective ones of said separate spectra.
 5. A diffractive opticalelement device as disclosed in claim 1, characterised in that thespectral bands of said spectra extend in one direction in a plane of thespectra, and that at least one detector is movable in a directiontransverse to said one direction of the spectral bands.
 6. A diffractiveoptical element device as disclosed in claim 5, characterised in thatthe position of said at least one detector is adjustable along said onedirection of the spectral bands.
 7. A diffractive optical element deviceas disclosed in claim 1, characterised in that the spectral bands ofsaid spectra extend in one direction in a plane of the spectra, and thatthe position of the light source is adjustable along said one directionof said spectral bands.
 8. A diffractive optical element device asdisclosed in claim 7, characterised in that the light source emits lightthrough a fixed aperture; and that a rotating disc is arranged in frontof the aperture, the disc being equipped with at least one slit or aplurality of minute holes, so that light passes through the slit or saidholes whilst the slit or the holes, because of their arc-shapedarrangement on the disc, move across the length of the aperture as thedisc rotates.
 9. A diffractive optical element device as disclosed inclaim 7, characterised in that the light source emits light via anoptical fibre that is mechanically movable by exciting a piezoelectricelement to which the end portion of the light fibre is attached.
 10. Adiffractive optical element device as disclosed in claim 1,characterised in that the spectral bands of said spectra extend in onedirection in a plane of the spectra, and that at least two detectors arearranged in the direction of the spectral bands of said spectra.
 11. Adiffractive optical element device as disclosed in claim 10,characterised in that the output from said at least two detectors iscollected by time-multiplexing.
 12. A diffractive optical element deviceas disclosed in claim 1, characterised in that a light deflectingelement comprising a tiltable mirror, is disposed in the light pathbetween the light source and the diffractive optical element.
 13. Adiffractive optical element device as disclosed in claim 1,characterised in that a light deflecting element comprising a tiltablemirror, is disposed in the light path between the diffractive opticalelement and the detector.
 14. A diffractive optical element device asdisclosed in claim 1, characterised in that spectral bands of saidspectra extend in one direction in a single plane, and that at least twodetectors are arranged in said one direction of the spectral bands. 15.A diffractive optical element device as disclosed in claim 1,characterised in that spectral bands of said spectra extend in onedirection in a single plane, and that at least two arranged in adirection transverse to said one direction of the spectral bands.
 16. Adiffractive optical element device as disclosed in claim 1,characterised in that spectral bands of said spectra extend in onedirection, and that at least two detectors are arranged in a directionorthogonal to a spectral band plane.
 17. A diffractive optical elementdevice as disclosed in claim 1, characterised in that the diffractiveoptical element is designed to change its diffraction efficiency whenmanipulated, and that the diffractive optical element has a binary levelsurface.
 18. A diffractive optical element device as disclosed in claim1, characterised in that the diffractive optical element consists of abase portion having a first pattern and a movable portion having areflective or differently patterned face; that the base portion and themovable portion have nominal spacing; that the diffractive opticalelement is arranged to change the nominal spacing when manipulated,thereby altering the diffraction efficiency of the diffractive opticalelement.
 19. A diffractive optical element device as disclosed in claim18 characterised in that the nominal spacing is nλ/2+λ/4, where n=1, 2,3 . . . , and where λ is the wavelength of the light.
 20. A diffractiveoptical element device as disclosed in claim 18, characterised in thatthe diffraction efficiency of the element is greatest at nλ/2+λ/4 andsmallest at nλ/2, where n=1, 2, 3 . . . , and where λ is the wavelengthof the light.
 21. A diffractive optical element device as disclosed inclaim 1, wherein the spectra are separate and offset relative to eachother.
 22. A diffractive optical element device as disclosed in claim 1,wherein the spectra are partly overlapping.
 23. A diffractive opticalelement device as disclosed in claim 1, wherein the spectra are separateand offset relative to each other and partly overlapping.
 24. Adiffractive optical element device as disclosed in claim 2,characterised in that the diffractive optical element is tiltable aboutat least a first axis, so that when the diffractive optical element istilted, said at least one detector is caused to detect a first set ofdifferent spectral regions in respective ones of said separate spectra.25. A diffractive optical element device as disclosed in claim 24characterised in that the diffractive optical element is tiltable abouta second axis that is orthogonal to the first axis, so that when thediffractive optical element is tilted, said at least one detector iscaused to detect at least a second set of different spectral regions inrespective ones of said separate spectra.
 26. A diffractive opticalelement device as disclosed in claim 2, characterised in that thespectral bands of said spectra extend in one direction in a plane of thespectra, and that at least one detector is movable in a directiontransverse to said one direction of the spectral bands.
 27. Adiffractive optical element device as disclosed in claim 26,characterised in that the position of said at least one detector isadjustable along said one direction of the spectral bands.
 28. Adiffractive optical element device as disclosed in claim 2,characterised in that the spectral bands of said spectra extend in onedirection in a plane of the spectra, and that the position of the lightsource is adjustable along said one direction of said spectral bands.29. A diffractive optical element device as disclosed in claim 28,characterised in that the light source emits light through a fixedaperture; and that a rotating disc is arranged in front of the aperture,the disc being equipped with at least one slit or a plurality of minuteholes, so that light passes through the slit or said holes whilst theslit or the holes, because of their arc-shaped arrangement on the disc,move across the length of the aperture as the disc rotates.
 30. Adiffractive optical element device as disclosed in claim 28,characterised in that the light source emits light via an optical fibrethat is mechanically movable by exciting a piezoelectric element towhich the end portion of the light fibre is attached.
 31. A diffractiveoptical element device as disclosed in claim 2, characterised in that alight deflecting element comprising a tiltable mirror, is disposed inthe light path between the light source and the diffractive opticalelement.
 32. A diffractive optical element device as disclosed in claim2, characterised in that a light deflecting element comprising atiltable mirror, is disposed in the light path between the diffractiveoptical element and the detector.
 33. A diffractive optical elementdevice as disclosed in claim 2, characterised in that the diffractiveoptical element is designed to change its diffraction efficiency whenmanipulated, and that the diffractive optical element has a binary levelsurface.
 34. A diffractive optical element device as disclosed in claim2, characterised in that the diffractive optical element consists of abase portion having a first pattern and a movable portion having areflective or differently patterned face; that the base portion and themovable portion have nominal spacing; that the diffractive opticalelement is arranged to change the nominal spacing when manipulated,thereby altering the diffraction efficiency of the diffractive opticalelement.
 35. A diffractive optical element device as disclosed in claim34 characterised in that the nominal spacing is nλ/2+λ/4, where n=1, 2,3 . . . , and where λ is the wavelength of the light which is related tothe function of the diffractive optical element.
 36. A diffractiveoptical element device as disclosed in claim 34, characterised in thatthe diffraction efficiency of the element is greatest at nλ/2+λ/4 andsmallest at nλ/2, where n=1, 2, 3 . . . , and where λ is the wavelengthof the light which is related to the function of the diffractive opticalelement.
 37. A diffractive optical element device as disclosed in claim3, wherein the spectra are separate and offset relative to each other.38. A diffractive optical element device as disclosed in claim 2,wherein the spectra are partly overlapping.
 39. A diffractive opticalelement device as disclosed in claim 2, wherein the spectra are separateand offset relative to each other and partly overlapping.
 40. Adiffractive optical element device for use in spectroscopy, whichcomprises a light source for emitting broadband light, a diffractiveoptical element towards which the light is emitted, and at least onedetector for receiving the light transmitted by the diffractive opticalelement, characterised in that the diffractive optical element consistsof at least two diffractive optical element parts that are related torespective wavelengths and produce at least two separate spectra or atleast two mutually partly overlapping spectra to give a compositespectrum, that optical deflecting means are disposed on or in connectionwith the diffractive optical element to produce in said spectrum anindication of wavelength value which indicates one or both of the upperand lower wavelength values, and that the diffractive optical element istiltable about at least a first axis, so that when the diffractiveoptical element is tilted said at least one detector is caused to detectsuccessively different spectral regions in said spectra or compositespectrum.
 41. A diffractive optical element device as disclosed in claim40, characterised in the spectral bands of said spectra extending in onedirection in a single plane of the spectra, and that said at least onedetector is movable in said one direction along the spectral bands ofsaid spectra or composite spectrum.
 42. A diffractive optical elementdevice as disclosed in claim 40, characterised in that spectral bands ofsaid spectra extend in one direction in a single plane, and that atleast two detectors are arranged in said one direction of the spectralbands.
 43. A diffractive optical element device as disclosed in claim40, characterised in that spectral bands of said spectra extend in onedirection in a single plane, and that at least two detectors arearranged in a direction transverse to said one direction of the spectralbands.
 44. A diffractive optical element device as disclosed in claim40, characterised in that spectral bands of said spectra extend in onedirection, and that at least two detectors are arranged in a directionorthogonal to a spectral band plane.
 45. A diffractive optical elementdevice for use in spectroscopy, which comprises a light source foremitting broadband light, a diffractive optical element towards whichthe light is emitted, and at least detector for receiving the lighttransmitted by the diffractive optical element, characterised in thatthe diffractive optical element has a plurality of diffractivedispersively focusing patterns which form fragments of the element, andwhose respective centres are two-dimensionally offset relative to eachother in order to produce a plurality of spectra where at least two areseparate, but offset relative to each other and/or partly overlapping;and that at least one of the fragments is attached to means so as tocause the fragment to be selectively mechanically manipulatable in orderto deform such a fragment, so that a generated spectrum either a) isbrought out of focus relative to a detector, or b) lies outside thedetection range of such a detector, or c) lies in focus for a seconddetector.
 46. A diffractive optical element device as disclosed in claim45, characterised in that the position of the light source isadjustable.
 47. A diffractive optical element device as disclosed inclaim 46, characterised in that the light source emits light through afixed aperture; and that a rotating disc is arranged in front of theaperture, the disc being equipped with at least one slit or a pluralityof minute holes, so that light passes through the slit or said holeswhilst the slit or the holes, because of their arc-shaped arrangement onthe disc, travel across the length of the aperture as the disc rotates.48. A diffractive optical element device as disclosed in claim 45,characterised in that the light source emits light via an optical fibrethat is mechanically movable by exciting a piezoelectric element towhich the end portion of the light fibre is attached.
 49. A diffractiveoptical element device as disclosed in claim 45, characterised in that alight deflecting element comprising a tiltable mirror, is disposed in alight path between the light source and the diffractive optical element.50. A diffractive optical element device as disclosed in claim 45,characterised in that a light deflecting element comprising a tiltablemirror, is disposed in a light path between the diffractive opticalelement and the detector.
 51. A diffractive optical element device asdisclosed in claim 45, characterised in that spectral bands of saidspectra extend in one direction in a single plane, and that at least twodetectors are arranged in said one direction of the spectral bands. 52.A diffractive optical element device as disclosed in claim 45,characterised in that spectral bands of said spectra extend in onedirection in a single plane, and that at least two detectors arearranged in a direction transverse to said one direction of the spectralbands.
 53. A diffractive optical element device as disclosed in claim45, characterised in that spectral bands of said spectra extend in onedirection, and that at least two detectors are arranged in a directionorthogonal to a spectral band plane.
 54. A diffractive optical elementdevice as disclosed in claim 45, characterised in that the diffractiveoptical element is designed to change its diffraction efficiency whenmanipulated, and that the diffractive optical element has a binary levelsurface.
 55. A diffractive optical element device as disclosed in claim45, characterised in that the diffractive optical element consists of abase portion having a first pattern and a movable portion having areflective or differently patterned face; that the base portion and themovable portion have nominal spacing; that the diffractive opticalelement is arranged to change the nominal spacing when manipulated,thereby altering the diffraction efficiency of the diffractive opticalelement.
 56. A diffractive optical element device as disclosed in claim55, characterised in that the nominal spacing is nλ/2+λ/4, where n=1, 2,3 . . . , and where λ is the wavelength of the light which is related tothe function of the diffractive optical element.
 57. A diffractiveoptical element device as disclosed in claim 55, characterised in thatthe diffraction efficiency of the element is greatest at nλ/2+λ/4 andsmallest at nλ/2, where n=1, 2, 3 . . . , and where λ is the wavelengthof the light which is related to the function of the diffractive opticalelement.
 58. A diffractive optical element device for use inspectroscopy, which comprises a light source for emitting broadbandlight, a diffractive optical element towards which the light is emitted,and at least one detector for receiving the light transmitted by thediffractive optical element, characterised in that the diffractiveoptical element has a plurality of diffractive dispersively focusingpatterns which form fragments of the element, and whose respectivecentres are two-dimensionally offset relative to each other in order toproduce a plurality of spectra where at least two are separate, butoffset relative to each other and/or partly overlapping; and that atleast one of the fragments is associated with means for causing thefragment to be selectively manipulatable through light controllablyblocking light reflection from the fragment.
 59. A diffractive opticalelement device as disclosed in claim 58, characterised in that theposition of the light source is adjustable.
 60. A diffractive opticalelement device as disclosed in claim 59, characterised in that the lightsource emits light through a fixed aperture; and that a rotating disc isarranged in front of the aperture, the disc being equipped with at leastone slit or a plurality of minute holes, so that light passes throughthe slit or said holes whilst the slit or the holes, because of theirarc-shaped arrangement on the disc, travel across the length of theaperture as the disc rotates.
 61. A diffractive optical element deviceas disclosed in claim 58, characterised in that the light source emitslight via an optical fibre that is mechanically movable by exciting apiezoelectric element to which the end portion of the light fibre isattached.
 62. A diffractive optical element device as disclosed in claim58, characterised in that spectral bands of said spectra extend in onedirection in a single plane, and that at least two detectors arearranged in said one direction of the spectral bands.
 63. A diffractiveoptical element device as disclosed in claim 58, characterised in thatspectral bands of said spectra extend in one direction in a singleplane, and that at least two detectors are arranged in a directiontransverse to said one direction of the spectral bands.
 64. Adiffractive optical element device as disclosed in claim 58,characterised in that spectral bands of said spectra extend in onedirection, and that at least two detectors are arranged in a directionorthogonal to a spectral band plane.
 65. A diffractive optical elementdevice as disclosed in claim 58, characterised in that a lightdeflecting element comprising a tiltable mirror, is disposed in a lightpath between the light source and the diffractive optical element.
 66. Adiffractive optical element device as disclosed in claim 58,characterised in that a light deflecting element comprising a tiltablemirror, is disposed in a light path between the diffractive opticalelement and the detector.
 67. A diffractive optical element device asdisclosed in claim 58, characterised in that the diffractive opticalelement is designed to change its diffraction efficiency whenmanipulated, and that the diffractive optical element has a binary levelsurface.
 68. A diffractive optical element device as disclosed in claim58, characterised in that the diffractive optical element consists of abase portion having a first pattern and a movable portion having areflective or differently patterned face; that the base portion and themovable portion have nominal spacing; that the diffractive opticalelement is arranged to change the nominal spacing when manipulated,thereby altering the diffraction efficiency of the diffractive opticalelement.
 69. A diffractive optical element device as disclosed in claim68, characterised in that the nominal spacing is nλ/2+λ/4, where n=1, 2,3 . . . , and where λ is the wavelength of the light which is related tothe function of the diffractive optical element.
 70. A diffractiveoptical element device as disclosed in claim 68, characterised in thatthe diffraction efficiency of the element is greatest at nλ/2+λ/4 andsmallest at nλ/2, where n=1, 2, 3 . . . , and where λ is the wavelengthof the light which is related to the function of the diffractive opticalelement.
 71. A diffractive optical element device for use inspectroscopy, which comprises a light source for emitting broadbandlight, a diffractive optical element towards which the light is emitted,and at least one detector for receiving the light transmitted by thediffractive optical element, characterised in that the diffractiveoptical element consists of at least two diffractive optical elementparts which are related to respective wavelengths and which produce atleast two separate spectra or at least two mutually partly overlappingspectra to give a composite spectrum, where at least one of thediffractive optical element parts is attached to a means for causing thediffractive optical element part to be selectively manipulatablemechanically in order to deform such diffractive optical element part,so that a generated spectrum either a) is brought out of focus relativeto a detector, or b) lies outside the detection range of such adetector, or c) lies in focus for a second detector.
 72. A diffractiveoptical element device for use in spectroscopy, which comprises a lightsource for emitting broadband light, a diffractive optical elementtowards which the light is emitted, and at least one detector forreceiving the light transmitted by the diffractive optical element,characterised in that the diffractive optical element consists of atleast two diffractive optical element parts which are related torespective wavelengths and which produce at least two separate spectraor at least two mutually partly overlapping spectra to give a compositespectrum, where at least one of the diffractive optical element parts isattached to means for causing the diffractive optical element part to beselectively manipulatable through light controllably blocking lightreflection from the element part.